Contact the company, where u want to send the email and check if their system is ok or not.
If the system is ok, then ask them to clear their mailbox…. i.e. delete some unnecessary messages, it might be that, mailbox is overloaded and ur mail is bouncing. One way u can check, again send the same mail to the same email id and also send the same to ur own email id…. next go to sent folder and check is it there! Perhaps, the email address is changed or u mistyped it. Please, check in all respect.